A basket-type induction motor is simple and strong, so that it is highly reliable and conventionally most commonly used in industry. However, in recent years, a synchronous motor using permanent magnets that has high efficiency and obtains high torque has attracted attention from the viewpoint of energy savings. A synchronous rotary electromotor which is a type of synchronous motor or a synchronous generator is structured to generate a rotating magnetic field by supplying an electric current to the coils of a stator, and rotate a rotor by applying this rotating magnetic field to a fixed magnetic field of the rotor. There are an SPM motor (Surface Permanent Magnet Motor) including permanent magnets attached to the outer peripheral surface of a rotor and an IPM motor (Interior Permanent Magnet Motor) including permanent magnets embedded in a rotor. Not only for such synchronous motors but also for all synchronous rotary electric machines including synchronous generators, a structure of a rotor capable of reducing an eddy current loss, reducing heat generation, and improving the rotation efficiency, has been studied and developed. Some inventions and devices relating to this have already been disclosed.
For example, Japanese Application Laid-Open Publication No. H11-98729 discloses an invention relating to a structure of a rotor capable of reducing an eddy current loss and improving an output of an electric motor, titled “Rotor structure of synchronous motor.”
The invention disclosed in the Publication No. H11-98728 noted above provides a structure in which more magnets than the number of magnetic poles are disposed on the outer peripheral portion of a rotor core in a state where the magnets are insulated from each other.
An eddy current loss is in proportion to the size of the magnets, so that with this structure, an eddy current loss that occurs in the magnets can be reduced. Accordingly, the output of the electric motor is improved.
Japanese Application Laid-Open Publication No. H10-225032 discloses an invention relating to a rotor of a permanent magnet type rotary electromotor including a shrink ring whose eddy current loss is extremely small, titled “Rotor of permanent magnet type rotary electromotor and manufacturing method for the same.”
The rotor that is the invention disclosed in the Publication No. H10-225032 noted above is structured so that, on the outer circumference of a wedge-shaped rotary shaft whose center portion is inclined in the axial direction, spacers and permanent magnets that are inclined in the same manner are disposed, and onto the outer side of these, a shrink ring that is also inclined and made of fiber reinforced plastic is fit.
The electrical conductivity of the fiber reinforced plastic is lower than that of stainless steel, so that with this structure, an eddy current loss can be made smaller than in the case of using a shrink ring made of stainless steel.
However, in the conventional technology described in the Publication No. H11-98728 noted above, although the eddy current loss occurring in the magnets can be reduced, the attaching area of the magnets to the rotor core is small, so that the magnets easily fly due to a centrifugal force when they rotate at a high speed.
In the conventional technology described in the Publication No. H10-225032 noted above, magnets and spacers must be processed into complicated shapes, so that the manufacturing cost is high.
The present invention was made in view of the conventional circumstances, and an object thereof is to provide a permanent magnet embedded rotor capable of improving rotation efficiency by reducing an eddy current loss, and being manufactured inexpensively.